This invention relates generally to gas generating materials such as used in the inflation of inflatable devices such as inflatable vehicle occupant restraint airbag cushions and, more particularly, to ignition enhanced gas generating materials.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as an "inflator."
Many types of inflator devices have been disclosed in the art for use in the inflating of one or more inflatable restraint system airbag cushions. Many prior art inflator devices include solid form gas generant materials which are burned to produce or form gas used in the inflation of an associated airbag cushion.
Gas generant compositions commonly utilized in the inflation of automotive inflatable restraint airbag cushions have previously most typically employed or been based on sodium azide. Such sodium azide-based compositions, upon initiation, normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving the safe and effective handling, supply and disposal of such gas generant materials.
Further, such inflator devices tend to involve rather complex ignition processes. For example, it is relatively common to employ an electrically initiated squib to ignite a separate charge of an igniter composition. The products of such ignition are then used to ignite a gas generant material, also contained within the inflator device. In practice, the ignition process of many various prior inflator devices require a separate igniter charge because the squib does not itself generally supply sufficient hot gas, condensed phase particles or other ignition products to sufficiently heat the gas generant material to result in the reaction of the material and desired gas generation.
As is known, the inflator incorporation of an ignition cord is a common means of obtaining substantially simultaneous ignition of an extended length of a charge of an igniter composition. In practice, it is common that such length of ignition cord be housed or contained within an igniter tube extending within the igniter charge. While ignition of the gas generant material may ultimately be achieved through the use of such an igniter charge, such an ignition process may be undesirably complicated and may tend to undesirably complicate the manufacture, production and design of the associated inflator device as well. For example, such use necessitates that an igniter composition be manufactured or made and then subsequently handled such as through manufacture of a desired form of container to hold or store the igniter composition for subsequent incorporation into the inflator device design as a part of an igniter assembly.
In addition, the use of such an ignition process can detrimentally impact either or both the weight and cost of the corresponding apparatus hardware. For example, the incorporation and use of such an igniter tube and ignition cord will typically increase both the weight and cost associated with a corresponding assembly.
As will be appreciated, space is often at a premium in modem vehicle designs. Consequently, it is generally desired that the space requirements for various vehicular components, including inflatable vehicle occupant restraint systems, be reduced or minimized to as great an extent as possible. The incorporation of an igniter assembly such as described above and associated support structure(s), may require a larger than desired volume of space within an associated inflator device. In particular, such volume of space could alternatively potentially be utilized to store or contain gas generant material and thereby permit the volume of space required by the inflator device to be reduced.
Thus, there is a need and a demand for alternative airbag inflator device ignition schemes and, in particular, there is a need and a demand for avoiding the requirement or inclusion of separate igniter composition charges and associated hardware. Various patents, including U.S. Pat. Nos. 4,698,107; 4,806,180; and 5,034,070, disclose processing wherein an ignition coating is applied, such as in the form of a liquid or a water slurry, to azide-based gas generant materials. Such processing typically necessitates first the formation of the azide-based gas generant, including the proper forming and drying of gas generant grains in selected shapes, followed by the coating of the grain with a wet slurry of the ignition material, such as by immersion of the grain in a slurry of the coating material, and then final drying.
In such dip coat processing, generally either individual gas generant tablets or wafers are coated as they go through a coating slurry on a conveyer belt, or the gas generant tablets or wafers are put in bulk containers and submerged in the slurried coating material. These types of process are typically relatively slow and may lead to problems such as coated tablets/wafers sticking either or both to themselves and associated equipment, such as conveyer belts.
In addition, dependent on the shape of the gas generant tablet or wafer there may also be a problem in obtaining application of a uniform coating. For example, if the gas generant material has a relatively flat form, the slurry coating may tend to pool and may therefore dry to form a coating of variable thicknesses.
Also, dip coating equipment (e.g., dip baskets and conveyer belts) may easily be contaminated with igniter material, leading to potential or increased safety concerns.
In view of the above, there is a need and a demand for materials and processing techniques such as avoid the requirement or inclusion of a separate igniter composition charge and which desirably simplify and/or facilitate manufacture, production or use.
Testing has shown that in the formation of ignition enhanced forms of at least certain gas generant materials, only a relatively narrow range of moisture content may be permitted. For example, an insufficient gas generant moisture level or content may result in an ignition composition failing to desirably adhere or join with the gas generant material. Correspondingly, an excessive or too great a moisture level or content may result in the formation of an ignition inhibiting surface or coating on the gas generant material rather than a desired ignition enhancing surface. In particular, those gas generant compositions which lack an effective binder component appear to have a particularly limited or narrow range of allowable moisture content for obtaining or resulting in an ignition enhanced gas generant having a coating or other suitable ignition enhancing material surface.
Thus, there is a need and demand for alternatives to azide-based pyrotechnics and related gas generants as well as for alternative improved ignition enhanced gas generating materials such as used in the inflation of inflatable devices such as an inflatable vehicle occupant restraint airbag cushions and related methods of processing such as may permit or facilitate the placement of an ignition composition onto a gas generant material having a selected form. In particular, there is a need and a demand for ignition enhanced gas generating materials and related processing methods wherein the gas generant material itself has a relatively low moisture content or level and/or lacks an effective binder component and such as may further desirably avoid the requirement or inclusion of a separate or distinct igniter composition charge.